DE69231669T2 - Device for processing an image signal - Google Patents

Description

The invention relates to an image signal processing device for processing an image signal.

A color coding device for modulating baseband color difference signals into a chrominance signal has been known as an example of an image signal processing device for processing an image signal.

Such a color coding device has a circuit arrangement such as that shown in Fig. 1. According to the circuit arrangement shown, burst flags (RY · BF and BY · BF) are added to baseband color difference signals (RY and BY according to Fig. 1) by burst adding circuits 41 and 42, respectively, and the output signals of the burst adding circuits 41 and 42 are clamped by clamping circuits 43 and 44, respectively. The output signals of the respective clamping circuits 43 and 44 are balanced modulated in push-pull modulation devices 45 and 46 using subcarrier signals SC90 and SC that are 90° out of phase with one another, and the output signals of the push-pull modulation devices 45 and 46 are added together in an adding device 47, whereby a chrominance signal or color value signal to which the Burst signals have been added, is formed from the baseband color difference signals.

Another circuit arrangement of the color coding device is shown in Fig. 2. In the circuit arrangement shown, the baseband color difference signals (R-Y and B-Y according to Fig. 2) are clamped by clamping circuits 51 and 52, respectively, and the output signals of the respective clamping circuits 51 and 52 are push-pull modulated in push-pull modulation devices 53 and 54 using the subcarrier signals SC90 and SC which are shifted in phase by 90°. Thereafter, the output signals of the push-pull modulation devices 53 and 54 are added together in an adder 55, whereby the baseband color difference signals are formed into a color value signal or chrominance signal. Meanwhile, a burst flag BF is subjected to quadrature two-phase modulation separately from the baseband color difference signals by a quadrature two-phase modulation means 56, thereby forming a burst signal. The burst signal is added to the chrominance signal output from the adder 55 in an adder 57. However, each of the above-mentioned known circuits has a number of disadvantages.

For example, each circuit requires a specific circuit block for adding burst signals to a chrominance signal. According to the circuit in Fig. 1, it is necessary to adjust the DC levels of the burst flags to those of the color difference signals or to adjust the bias levels of the color difference signals and the burst flags when the burst flags are to be added to the According to the circuit of Fig. 2, it is necessary to form various burst signals to be added to a chrominance signal according to the discrimination of whether a chrominance signal to be formed conforms to the NTSC television system or the PAL television system. Particularly, if a chrominance signal conforming to the PAL television system is to be formed, the phase of the burst signal must be switched, so that a circuit having a complicated arrangement is required and therefore it is difficult to adjust the circuit.

GB-A-2 124 450 discloses a hue control circuit. The hue control circuit includes a first push-pull modulation device for receiving a first colour difference signal, a second push-pull modulation device for receiving a second colour difference signal, an oscillator 1 for generating a subcarrier signal and a phase shifting device for shifting the subcarrier signal by 90°. The subcarrier signal and the phase-shifted subcarrier signal are respectively supplied to the two push-pull modulation devices and are used to modulate the two colour difference signals. A burst flag is added to each of the colour difference signals, this addition being carried out by an adder device arranged before or separately from the push-pull modulation device. Therefore, an additional circuit is necessary for each of the colour difference signals.

Patent Abstracts of Japan, Vol. 10, No. 386 (E-467) (2443), December 24, 1986 & JP-A-61 177 006 (Sony Corp.), August 8, 1983 discloses an AM modulation device, which is used to modulate an input video signal and an input audio signal by using differential amplifiers. It is not shown to use the differential amplifiers to add a burst signal to a color difference signal.

Patent Abstracts of Japan, Vol. 5, No. 55 (E-52) (727) 16 April 1981 & JP-A-56 006 504 (Sony K. K.), 23 January 1981 (D3) discloses a push-pull modulation device with four differential amplifiers.

EP-A-0 310 963 (Fuji Photo Film Co., Ltd.) discloses a circuit for generating a chrominance signal from a line sequential color difference signal. From this line sequential color difference signal, two color difference signals are obtained and processed by clamping circuits and modulating means. A burst signal is added to a color difference signal using an adder.

It is therefore an object of the invention to provide an image signal processing device which makes it possible to solve the above-mentioned problems and further to provide an image signal processing device which can add a burst signal to a color difference signal and modulate the resulting sum signal by means of a simple arrangement without the need for complicated adjustment and without the need to provide an additional adding circuit.

Another object of the invention is to provide an image signal processing apparatus which converts burst signals into a chrominance signal by means of a simple arrangement and without the need for complicated adjustment.

The object is achieved by an image signal processing device according to the independent claims 1 and 5. Further advantageous modifications are set out in the dependent claims.

The object, features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments of the invention with reference to the attached drawings.

Show it:

Fig. 1 is a block diagram showing the basic arrangement of a conventional color coding device with burst signal adding circuits,

Fig. 2 is a block diagram showing the basic arrangement of another conventional color coding device with burst signal adding circuits,

Fig. 3 is a circuit diagram showing the arrangement of a burst signal adding circuit to which an embodiment of the invention is applied,

Fig. 4 is a block diagram for illustrating the basic arrangement of a color coding device to which the burst signal adding circuit according to Fig. 3 is applied, and

Fig. 5 is a circuit diagram illustrating a burst signal adding circuit to which another embodiment of the invention is applied.

Preferred embodiments of the invention are described below with reference to the drawing.

Fig. 3 is a circuit diagram showing a burst signal adding circuit to which an embodiment of the invention is applied.

The circuit according to Fig. 3 includes transistors Q1 to Q8, resistors R1 to R4, constant current sources I1 to I9, a power supply VCC, a reference power supply REF, an input terminal IN1 for inputting a baseband color difference signal, an input terminal IN2 for inputting a burst flag, an input terminal SC for inputting a subcarrier signal, an input terminal SC' for inputting a phase-inverted subcarrier signal and an output terminal OUT for outputting a modulated signal.

In the circuit of Fig. 3, the transistors Q1 and Q2, the resistor R1 and the constant current sources 11 and 12 form a first differential amplifier. One input terminal of the first differential amplifier is connected to the reference power supply REF and the other input terminal of the first differential amplifier is connected to the input terminal IN1 for inputting a baseband color difference signal.

The transistors Q3 and Q4, the resistor R2 and the constant current sources 13 and 14 form a second differential amplifier. One input terminal of the second differential amplifier is connected to the reference power supply REF and the other input terminal of the second differential amplifier is connected to the input terminal IN2 for inputting a burst flag.

The output signals of the first differential amplifier and the second differential amplifier are fed to common signal lines.

The resistor R3 is connected to the transistors Q5 and Q7 as a common load resistor, while the resistor R4 is connected to the transistors Q6 and Q8 as a common load resistor. The transistors Q5 and Q6 are connected to the respective resistors R3 and R4 to form a third differential amplifier. The transistors Q7 and Q8 are also connected to the respective resistors R3 and R4 to form a fourth differential amplifier. An input terminal of each of the third and fourth amplifiers is connected to an associated one of the common signal lines to which the respective output signals of the first and second differential amplifiers are supplied. The other input terminals of the third and fourth amplifiers are connected to the input terminals SC and S5', respectively. The connection point of the resistor R3 and the transistors Q5 and Q7 is connected to the output terminal OUT.

Fig. 4 shows a block diagram for the basic illustration of the arrangement of a color coding device to which the burst signal adding circuit according to Fig. 3 is applied. In Fig. 4, a part containing a clamp circuit 21 and a push-pull modulation device 23 and a part containing a clamp circuit 22 and a push-pull modulation device 24 each correspond to the arrangement according to Fig. 3.

As shown in Fig. 4, a color difference signal R-Y and a burst flag R-Y · BF are clamped at a reference voltage (REF) in the clamp circuit 21, whereas a color difference signal B-Y and a burst flag B-Y · BF are clamped at the reference voltage (REF) in the clamp circuit 22. The output signals of the clamp circuits 21 and 22 are respectively subjected to push-pull modulation in the push-pull modulation means 23 and 24 using subcarrier signals SC90 and SC which are 90° out of phase with each other. Thereafter, the output signals of the push-pull modulation means 23 and 24 are supplied to an adder 25. The adder 25 adds the input signals together and outputs a chrominance signal to which burst signals have been added.

According to the arrangement of Fig. 3, the color difference signal (R- Y or B-Y) input through the input terminal TN1 is converted into a current by the resistor R1, while the burst flag (R-Y · BF or B-Y · BF) is converted into a current by the resistor R2.

The color difference signal converted into current is output as the collector current of each of the differential transistors Q1 and Q2, while the burst flag converted into current is output as the collector current of each of the differential transistors Q3 and Q4. The collector currents of the differential transistors Q1 and Q3 are added together and the resulting current is supplied to the differential transistors Q5 and Q6 as a bias current. Similarly, the collector currents of the differential transistors Q2 and Q4 are added together and the resulting current is supplied to the differential transistors Q7 and Q8 as a bias current.

These bias currents are represented by the following expressions. The bias current for the differential transistors Q5 and Q6 is:

Ia = 21-(Vc/R1+Vb/R2)

and the bias current for the

Differential transistors Q7 and Q8 correspond to:

Ib = 21+(Vc/R1+Vb/R2)

where Vc corresponds to the color difference signal and Vb corresponds to the burst flag.

Each of the bias currents is modulated by the subcarrier signals (SC and SC') and the modulated currents are fed from the Differential transistors Q5 and Q7 are supplied to the resistor R3, while the modulated currents from the differential transistors Q6 and Q8 are supplied to the resistor R4. The supplied currents are converted into a voltage by the resistors R3 and R4 and the resulting voltage is then output as a signal through the output terminal OUT.

The voltage of the signal output by the output terminal OUT corresponds to:

Vout = VCC-(2R4 · I+R4(Vc/R1+Vb/R2)},

if SC = H and SC' = L,

or if SC = L and SC' = H

Vout = VCC-{2R4 · I-R4(Vc/R1+Vb/R2)}.

The gain of the color difference signal is determined by a value R4/R1 and the gain of the burst flag is determined by a value R4/R2.

The modulated signal obtained by adding the burst flag to the color difference signal and modulating the sum signal in the manner described above is output from the output terminal OUT of Fig. 3 to the adder 25 of Fig. 4, that is, the modulated signal obtained by adding the burst flag RY · BF to the color difference signal RY and modulating the sum signal and the modulated signal obtained by adding the burst flag BY · BF to the color difference signal BY and modulating the sum signal are output to the adder 25 of Fig. 4. The adder 25 adds the input modulated signals together and outputs the sum signal as a color signal or chrominance signal.

As is apparent from the above description, according to the arrangement described above as an embodiment, there is no need to include an independent circuit block for adding the burst signal R-Y · BF (or B-Y · BF) since the modulation of the color difference signal R-Y (or B-Y) and the addition of the burst signal R-Y · BF (or B-Y · BF) to the color difference signal R-Y (or B-Y) are carried out in a single circuit arrangement. The amplitude of each of the burst signals R-Y · BF and B-Y · BF of the formed chrominance signal can be easily controlled by adjusting the amplitude of the burst flag input through the input terminal IN2 as shown in Fig. 3. Furthermore, by selectively enabling or prohibiting the input of the burst flag R-Y · BF as shown in Fig. 4, a chrominance signal conforming to the NTSC television system or the PAL television system can be easily formed. Furthermore, when a chrominance signal conforming to the PAL television system is to be formed, the phases of the respective burst signals of the chrominance signal can be easily controlled by changing the amplitude ratio of the burst flag R-Y · BF to the burst flag B-Y · BF shown in Fig. 4.

Fig. 5 is a circuit diagram showing a burst signal adding circuit to which another embodiment of the invention is applied.

In Fig. 5, the same reference numerals are used to designate components that are are essentially identical to the components shown in Fig. 3, which is why a detailed description is omitted.

In the circuit according to Fig. 5, components 15 and 16 represent constant current sources, each supplying a current 2·I.

The arrangement of Fig. 5 differs from the arrangement of Fig. 3 in that a modulated signal is output as a current through the output terminal OUT. The output current is represented by the following equations:

If SC = H and SC' = L, then:

Iout = Vc/R1+Vb/R2.

If SC = L and SC' = H, then:

Iout = -(Vc/R1+Vb/R2).

Then, modulated signals obtained by adding the respective burst flags R-Y · BF and B-Y · BF to the color difference signals R-Y and B-Y are output to the adder 25. After the input modulated signals are added together to form a current sum signal, the current sum signal is converted into a voltage signal in the adder 25, and the voltage signal is output as a chrominance signal.

As can be seen from the above description, in the arrangement according to the embodiment described above, a simple circuit arrangement can be adopted since there is no need to include an independent circuit block for adding the burst signal RY · BF (or BY · BF) to the color difference signal RY (or β-Y). In addition, adjustment is facilitated since the amplitude and phase of each of the burst signals of the chrominance signal can be adjusted by controlling the amplitudes of the input burst flags.

As is apparent from the above description, according to the above-described embodiment, an image signal processing apparatus can be provided which can add burst signals to a chrominance signal by means of a simple arrangement and without the need for complicated adjustment.

An image signal processing apparatus according to the invention is an apparatus for processing an image signal. The apparatus is provided with first differential amplifying means for receiving a color difference signal and a reference signal, second differential amplifying means for receiving a burst flag signal and the reference signal, and modulating means for jointly receiving signals output by the first and second differential amplifiers and modulating the received signals by using a carrier signal. Accordingly, it is possible to add the burst flag signal to the color difference signal and modulate the obtained sum signal by means of a simple means and without the need for complicated adjustment.

Claims (7)

1. Image signal processing device for processing an image signal, comprising: (A) a first differential amplifier (Q1, Q2, R1, 11, 12) for receiving a color difference signal (IN1) and a reference signal (REF), (B) . a second differential amplifier (Q3, Q4, R2, 13, 14) for receiving a burst flag signal (IN2) and the reference signal (REF) and (C) a modulation device comprising a third differential amplifier (Q5, Q6) and a fourth differential amplifier (Q7, Q8), wherein each of the differential amplifiers has two transistors, the collector of a transistor (Q1) of the first differential amplifier and the collector of a transistor (Q3) of the second differential amplifier are connected to one another and to a first common signal line (Ia) and the collector of the further transistor (Q2) of the first differential amplifier and the collector of the further transistor (Q4) of the second differential amplifier are connected to one another and to a second common signal line (Ib), and the third and the fourth differential amplifier each receive a carrier signal (SC) and a phase-inverted signal (SC') of the carrier signal, the emitters of the Transistors of the third differential amplifier are connected to each other and to the first common signal line, the emitters of the transistors of the fourth differential amplifier are connected to each other and to the second common signal line, and the collector of a transistor (Q5) of the third differential amplifier and the collector of a transistor (Q7) of the fourth differential amplifier are connected to each other and to an output terminal (OUT) for outputting a modulated signal. 2. An image signal processing device according to claim 1, wherein a base of one (Q2) of the two transistors of the first differential amplifier is supplied with the color difference signal (IN1) and an emitter of the one transistor (Q2) is connected to a current source (12), while a base of the other (Q1) of the two transistors is supplied with the reference signal (REF) and an emitter of the other transistor (Q1) is connected to a current source (11). 3. Image signal processing device according to claim 1 or 2, wherein a base of one (Q4) of the transistors of the second amplifier is supplied with the burst flag signal (IN2) and an emitter of the one transistor (Q4) is connected to a current source (14), while a base of the other (Q3) of the two transistors is supplied with the reference signal (REF) and an emitter of the other transistor (Q3) is connected to a current source (13). 4. Image signal processing apparatus according to one of the preceding claims, wherein the modulation means is arranged to be controlled by the respective first and to push-pull modulate the signals supplied to the second differential amplifier using the carrier signal. 5. An image signal processing device for processing an image signal, comprising two image signal processing devices according to claim 1, wherein the first image signal processing device (21, 23 of Fig. 4) receives an R-Y signal and a burst flag signal (R-Y · BF) and the second image signal processing device (22, 24 of Fig. 4) receives a B-Y signal and a burst flag signal (B-Y · BF), and an adder (25) for adding the output signals of the two image signal processing devices to form a chrominance signal, wherein the modulation device (23) of the first image signal processing device receives a first carrier signal (SC90) and the modulation device (24) of the second image signal processing device receives a second carrier signal (SC), wherein the first carrier signal for the first image signal processing device is 90° out of phase with the second carrier signal for the second image signal processing device. 6. Image signal processing device according to claim 5, wherein the modulation device (23) of the first image signal processing device is arranged to push-pull modulate the signal output from the first and second differential amplifiers of the first image signal processing device (21, 23) using the first carrier signal (SC90). 7. Image signal processing device according to claim 5, wherein the modulation device of the second image signal processing device (24) is arranged to push-pull modulate the signal output from the first and second differential amplifiers of the second image signal processing device (22, 24) by using the second carrier signal (SC).